Page:The Eurypterida of New York Volume 1.pdf/387



Pohlman. Buffalo Soc. Nat. Hist. Bul. 1883. 4: 19, fig. 5

The waterlime at Buffalo has furnished the broad symmetrical remains of a creature described by Pohlman as the carapace of a gigantic Ceratiocaris on the assumption that the two semicircular valves of this supposed phyllocarid had been spread out on both sides of the dorsal line. This view is clearly erroneous and the fossil is the telson of a Pterygotus. According to Pohlman it was found in the same bed which yielded the Pterygotus. The specimen represents the section with bilobed telson (Erettopterus). , a British Ludlow form, possessed a similar telson [Huxley & Salter, Monogr. pl. 12, fig. 45] although it is considerably surpassed in transverse development by this American species.

As a telson this fossil is characterized by the anterior transverse hinge line where it is connected with the preceding segment, the man smooth antelateral edge and the scalloped postlateral edge. The anterior half is provided with a median ridge while the posterior part is divided by a median cleft. It is probably the character of this median line which led to the reference of the fossil to Ceratiocaris.

The form of the telson is transversely elliptic with rather acute ends. Its major diameter, 24 cm, is to the minor as 12 : 7. The anterior hinge line is but 69 mm long, thus indicating the broad flaring character of the telson in comparison to the postabdomen. The scallops are broad and shallow; at the termination of the median line is a deeper and broader emargination. The sides of the median cleft are curved outward and overlap considerably. The surface is very finely granulated.

This telson must have been the effective propelling organ of a gigantic merostome, which was undoubtedly 5 feet or more in length. In view of